A swimmer practiced in a still water inlet a river made in its bank, and achieved a speed of 4 km/h. When she was swimming upstream in the river, however, she could only make 3 km/h. One day the swimmer swam into the river from the inlet, then doubled the covered distance going downstream, and finally came back. She averaged 3.8 km/h that day. What was her downstream speed?
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Philosophers have interpreted world in various ways, the point is to change it!
